1. Field of the Invention
The present invention relates to an electronic timepiece displaying time with hands and being equipped with a hand position detecting mechanism.
2. Description of Related Art
In an electronic timepiece driving its hands with a stepping motor, for example, if a strong magnet is situated in the vicinity of the electronic timepiece, the rotor of the stepping motor does sometimes not rotate although drive pulses are supplied, and the hands are not driven.
An electronic timepiece equipped with a function of detecting the positions of its hands has conventionally been proposed (see, for example, Japanese Patent Application Laid-Open Publication No. 2009-085674), which timepiece detected the positions by forming a penetration hole in each of the gears rotating in conjunction with the hands, respectively, and setting the penetration holes to appear at a detection position when the hands were situated at a predetermined position to detect the penetration holes with a photointerrupter or the like and thereby to detect the positions of the hands.
The hand position detecting mechanism disclosed in Japanese Patent Application Laid-Open Publication No. 2009-085674 has been capable of performing the position detection of the hands only once for an hour at the time of an ordinary hand movement. For example, even if a positional shift of its second hand has been caused, the positional shift has sometimes not been capable of being detected for a long time nearly to one hour or so forth.
Moreover, if the hand position detecting mechanism is adapted to execute hand position detection every one second or every two seconds in order to detect the positional shift of the second hand, then the hand position detecting mechanism produces a problem in which the number of times of detection becomes very large and excessive electric power is consumed.
Moreover, if the hand position detecting mechanism is adapted to execute the hand position detection only at the timing at which the penetration holes of the gears appear at the detection position, then a situation in which it is impossible to detect a stopped state of the hands when the hands are stopped at the detection position owing to an external factor (for example, a strong magnet) arises.
Moreover, some electronic timepieces each include a hand position counter therein to count the rotation positions of their hands on the basis of the number of drive times of each of their stepping motors besides their timing counters. In an electronic timepiece displaying information other than time with its hands temporarily and an electronic timepiece performing the detection and correction of the positional shifts of its hands, the hands sometimes move to positions different from those at the present time, such electronic timepieces each need also the hand position counter besides the timing counter.
When the hands are abnormally stopped owing to an external factor (for example, a strong magnet), the value of the hand position counter continues to be counted up every output of a drive pulse that brings about a presumption that the stepping motor has been driven, and consequently the value of the hand position counter gradually becomes apart from the value indicating the real hand positions.
In such a case, the value of the hand position counter can correctly be corrected at the time of a restart of a normal hand movement by previously counting the number of times of the detection of hand stops from the detection time of an abnormal stop of the hands to the next detection of the normal hand movement. That is, the value of the hand position counter can be corrected to a value indicating the real hand positions by subtracting the counted value for the number of times of the detection of hand stops from the value of the hand position counter at the time point of the detection of the normal hand movement.
However, an abnormal stop of the hands will sometimes extend over a long period of time, for example, in the case where an electronic timepiece is left as it is in the neighborhood of a strong magnet. In this case, if the number of times of the detection of hand stops is counted, the counted value will sometimes become a very large value. A counter having a relatively large number of bits (e.g. a storage region of a random access memory (RAM)) must be prepared for counting the number of times of the detection of hand stops in order to deal with such a long term hand stop. A counter having a small number of bits would overflow when the abnormal stop of the hands extends over a long period of time, and consequently the value of the hand position counter would become incapable of correcting the value normally.
The present invention provides an electronic timepiece capable of rapidly detecting the occurrence of a situation of a positional shift or an abnormal stop of a second hand, capable of reducing the number of times of detection operations to achieve a reduction of power consumption, and capable of easily correcting the value of a hand position counter when the rotation of the second hand stops without counting the number of times of the detection of hand stops and without needing a counter having a large number of bits.